Certain rare earth-transition metal containing alloys can be made permanently magnetic by quenching in a very finely crystalline microstructure. One method of doing this is to eject a fine stream of molten alloy through a small orifice and quench the stream on a rapidly moving chill surface such as the perimeter of a rotating metal quench wheel. This process is known as melt spinning or jet casting. These terms may be used interchangeably herein to refer to such rapid solidification processes. Methods of making rare earth-iron (RE-Fe) based permanent magnets using melt spinning techniques are set forth in U.S. Pat. No. 4,495,396, U.S. Ser. No. 414,936 filed Sept. 3, 1982 and U.S. Ser. No. 544,728 filed Oct. 26, 1983 to Croat assigned to the assignee hereof, for example.
One problem encountered in jet casting is the erosion of the orifice through which the molten metal is expressed. As the orifice erodes, a greater amount of metal passes through it. Eventually, the metal flows too quickly to be quenched rapidly enough to achieve a desired amorphous to very finely crystalline microstructure.